Hi Mariner..
.. My question is, is it any good for the type of music I have in mind?..

Peter Bellamy accompanied himself on anglo, but he had quite a high range. John Kirkpatrick also does, but he's an ace player, and able to play in many keys, which you won't be able to do with only 20 keys, although you could also play in D (but without the C#) and the associated minor keys (E,A,B) and some other modal ones . But, inspite of 'Hollywood' mythology, concertinas were probably never used by sailors!

The previous comments about the quality of the instrument are valid, if its the standard Chinese made 'new red box' usually seen in music shops.

...It is a different system than the one used in traditional music..
Many of the revival singers (ie 1960s on) use the English system to accompany themselves (Tony Rose comes to mind as an example). But for traditional music (William Kimber,Scan Tester,etc and numerous musicians in Ireland) the anglo, even with only 20 keys, was used.
..Then theres the degree of difficulty playing it..
Some people pick up the anglo and can play simple tunes straight away (its like a mouth organ). Others struggle. Its the same with the English system. Different folks, different strokes!
good luck ..wes.